Wilson, John S. (Downers Grove, IL)
Davis, Howard W. (Darien, IL)
Bisiules, Peter J. (LaGrange Park, IL)
Bibblecom, Charles A. (Naperville, IL)
Racana, Lawrence S. (Willow Brook, IL)
Ulery, David J. (Warrenville, IL)

09/172329

03/07/2000

10/14/1998

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Andrew Corporation (Orland Park, IL)

343/795

343/872, 343/797

H01Q1/24; H01Q9/28; H01Q21/08; H01Q9/04; H01Q9/28

343/795, 343/797, 343/789, 343/853, 343/906, 343/872, 343/702, 343/821

3496570	VAN ATTA ARRAY	February, 1970	Lewis
3680139	COMMON ANTENNA APERTURE HAVING POLARIZATION DIVERSITY	July, 1972	Reynolds, Jr.	343/756
3680143	SHAPED BEAM ANTENNA	July, 1972	Ajioka et al.	343/778
3681769	DUAL POLARIZED PRINTED CIRCUIT DIPOLE ANTENNA ARRAY	August, 1972	Perrotti et al.	343/814
3681771	RETROFLECTOR DIPOLE ANTENNA ARRAY AND METHOD OF MAKING	August, 1972	Lewis et al.	343/817
3718935	DUAL CIRCULARLY POLARIZED PHASED ARRAY ANTENNA	February, 1973	Ranghelli et al.	343/797
3720953	DUAL POLARIZED SLOT ELEMENTS IN SEPTATED WAVEGUIDE CAVITY	March, 1973	Ajioka	343/771
3740754	BROADBAND CUP-DIPOLE AND CUP-TURNSTILE ANTENNAS	June, 1973	Epis	343/797
3742506	DUAL FREQUENCY DUAL POLARIZED ANTENNA FEED WITH ARBITRARY ALIGNMENT OF TRANSMIT AND RECEIVE POLARIZATION	June, 1973	Wilkinson	343/854
3747114	PLANAR DIPOLE ARRAY MOUNTED ON DIELECTRIC SUBSTRATE	July, 1973	Shyhalla	343/795
3750185	DIPOLE ANTENNA ARRAY	July, 1973	Evans	343/814
3810185	DUAL POLARIZED CYLINDRICAL REFLECTOR ANTENNA SYSTEM	May, 1974	Wilkinson	343/756
3821742		June, 1974	Pollard	343/727
3922680	Space feed receiver array	November, 1975	Alsberg et al.	343/754
4015263	Dual polarized blade antenna	March, 1977	Koerner et al.	343/708
4031537	Collinear dipole array with reflector	June, 1977	Alford	343/704
4087818	Lossless network and method for orthogonalizing dual polarized transmission systems	May, 1978	Kreutel, Jr.	343/176
4180817	Serially connected microstrip antenna array	December, 1979	Sanford	343/700MS
4193077	Directional antenna system with end loaded crossed dipoles	March, 1980	Greenberg et al.	343/747
4223317	Dual polarization antenna couplets	September, 1980	Rod	343/803
4263598	Dual polarized image antenna	April, 1981	Bellee et al.	343/700MS
4340891	Dual polarized base station receive antenna	July, 1982	Phillips	343/713
4364050	Microstrip antenna	December, 1982	Lopez	343/700MS
4412222	Dual polarized feed with feed horn	October, 1983	Mohring et al.	343/779
4464663	Dual polarized, high efficiency microstrip antenna	August, 1984	Lalezari et al.	343/700MS
4472717	Intrapulse polarization agile radar system (IPAR)	September, 1984	Eaves et al.	343/5
4504836	Antenna feeding with selectively controlled polarization	March, 1985	Seavey	343/761
4518969	Vertically polarized omnidirectional antenna	May, 1985	Bogner	343/819
4571591	Three dimensional, orthogonal delay line bootlace lens antenna	February, 1986	Valentino et al.	343/754
4644562	Combined cross polarization interference cancellation and intersymbol interference equalization for terrestrial digital radio systems	February, 1987	Kavehrad et al.	375/14
4658262	Dual polarized sinuous antennas	April, 1987	DuHamel	343/792.5
4675685	Low VSWR, flush-mounted, adaptive array antenna	June, 1987	Finken	343/708
4695844	Device for receiving dual polarized microwave signals	September, 1987	Houchangnia	343/781CA
4710775	Parasitically coupled, complementary slot-dipole antenna element	December, 1987	Coe	343/727
4737793	Radio frequency antenna with controllably variable dual orthogonal polarization	April, 1988	Munson et al.	342/361
4772891	Broadband dual polarized radiator for surface wave transmission line	September, 1988	Svy	343/707
4821039	Dual polarized monopulse orthogonal superposition	April, 1989	Crane	342/153
4825220	Microstrip fed printed dipole with an integral balun	April, 1989	Edward et al.	343/795
4839663	Dual polarized slot-dipole radiating element	June, 1989	Kurtz	343/771
4870426	Dual band antenna element	September, 1989	Lamberty et al.	343/705
4929961	Non-grounded type ultrahigh frequency antenna	May, 1990	Nakase	343/715
4943811	Dual polarization electromagnetic power reception and conversion system	July, 1990	Alden et al.	343/814
5146234	Dual polarized spiral antenna	September, 1992	Lalezari	343/895
5157409	Cam lock antenna mounting assembly	October, 1992	Hamin	343/715
5172080	Garnet centering ring for circulators and isolators	December, 1992	Fisher et al.	333/1.1
5206655	High-yield active printed-circuit antenna system for frequency-hopping space radar	April, 1993	Caille et al.	343/700MS
5220330	Broadband conformal inclined slotline antenna array	June, 1993	Salvail et al.	343/705
5227807	Dual polarized ambidextrous multiple deformed aperture spiral antennas	July, 1993	Bohlman et al.	343/895
5268701	Radio frequency antenna	December, 1993	Smith	343/767
5274391	Broadband directional antenna having binary feed network with microstrip transmission line	December, 1993	Connolly	343/820
5309165	Positioner with corner contacts for cross notch array and improved radiator elements	May, 1994	Segal et al.	343/770
5319379	Parabolic dual reflector antenna with offset feed	June, 1994	Waken et al.	343/756
5321414	Dual polarization dipole array antenna	June, 1994	Alden et al.	343/816
5400042	Dual frequency, dual polarized, multi-layered microstrip slot and dipole array antenna	March, 1995	Tulinsteff	343/727
5451969	Dual polarized dual band antenna	September, 1995	Toth et al.	343/781CA
5453751	Wide-band, dual polarized planar antenna	September, 1995	Tsukamoto et al.	343/700MS
5481272	Circularly polarized microcell antenna	January, 1996	Yarsunas	343/797
5499033	Polarization diversity antenna	March, 1996	Smith	343/700MS
5534877	Orthogonally polarized dual-band printed circuit antenna employing radiating elements capacitively coupled to feedlines	July, 1996	Sorbello et al.	343/700MS
5589843	Antenna system with tapered aperture antenna and microstrip phase shifting feed network	December, 1996	Meredith et al.	343/820
5630226	Low-noise downconverter for use with flat antenna receiving dual polarized electromagnetic waves	May, 1997	Kanda et al.	343/756
5742258	Low intermodulation electromagnetic feed cellular antennas	April, 1998	Kumpfbeck et al.	343/795
5818397	Circularly polarized horizontal beamwidth antenna having binary feed network with microstrip transmission line	October, 1998	Yarsunas et al.	343/797

AU9228386	May, 1993
AU9527118	February, 1996
EP0416300	March, 1991			Dual polarized spiral antenna.
EP0464255	January, 1992			Multiband antenna.
EP0523770	January, 1993			Low-noise-block downconverter for use with flat antenna receiving dual polarized electromagnetic waves.
EP0566522	October, 1993			Antenna system and method of manufacturing said system.
EP0647977	April, 1995			Circularly polarized microcell antenna.
EP0657956	June, 1995			Antenna assembly.
EP0495507	November, 1995			Retractable motorized multiband antenna.
EP0715477	June, 1996			Modular interconnect matrix for matrix connection of a plurality of antennas with a plurality of radio channels units
EP0725498	August, 1996			Radio signal scanning and targeting system for use in land mobile radio base sites
EP0433255	January, 1997			Orthogonally polarized dual-band printed circuit antenna employing radiating elements capacitively coupled to feedlines.
FR1236535	June, 1959

Brian Edward and Daniel Rees, "A Broadband Printed Dipole With Integrated Balun" Microwave Journal May 1987 (pp. 339-344).
Willmar K. Roberts, "A New Wide-Band Balun" IRE, Jun. 1957 (pp. 1628-1631).

Wong, Don

Ho, Tan

Arnold White & Durkee

We claim:

1. An antenna for transmitting and receiving electromagnetic signals comprising:

a mounting plate having a longitudinal axis;

a plurality of dipole radiating elements projecting outwardly from a surface of said mounting plate, each of said radiating elements including a balanced orthogonal pair of dipoles aligned at first and second predetermined angles with respect to said longitudinal axis, forming crossed dipole pairs;

an unbalanced feed network electromagnetically coupled to said radiating elements; and

a plurality of microstrip hooks, each of said microstrip hooks being positioned adjacent to, and spaced from, each of said dipoles by a microstrip clip.

2. The antenna of claim 1, wherein said feed network extends along said mounting plate and is spaced from said mounting plate by a plurality of feed network clips.

3. The antenna of claim 2, wherein said feed network clips and said microstrip clip have the same configuration.

4. The antenna of claim 1, wherein said feed network includes microstrip transmission lines spaced from said mounting plate by a plurality of feed network clips.

5. The antenna of claim 1, wherein said microstrip clip is composed of a dielectric material.

6. The antenna of claim 1, wherein said microstrip clip includes two generally U-shaped projections extending upwardly from a base of said clip and two generally U-shaped projections extending downwardly from said base.

7. The antenna of claim 1, wherein said radiating elements are comprised of metal.

8. The antenna of claim 1, wherein said radiating elements are attached to said mounting plate such that each of said pairs of dipoles are generally orthogonal to said surface of said mounting plate.

9. The antenna of claim 1, wherein each of said radiating elements includes four half dipoles and each of said radiating elements includes a base with four feet.

10. The antenna of claim 9, wherein each of said feet is attached to said mounting plate by a cold forming method.

11. The antenna of claim 1, wherein said dipoles comprise two half dipoles, each of said half dipoles having a generally inverted L-shaped profile, a portion of said generally L-shaped profile forming a vertical support.

12. The antenna of claim 11, further including a balun comprised of one of said microstrip hooks and said vertical support for each half dipole.

13. The antenna of claim 12, wherein each said microstrip hook is separated from said vertical support for each half dipole by an air dielectric.

14. The antenna of claim 1, wherein each of said microstrip hooks is generally shaped like an inverted U.

15. The antenna of claim 1, whereby said first predetermined angle is substantially equal to +45 degrees with respect to said longitudinal axis and said second predetermined angle is substantially equal to -45 degrees with respect to said longitudinal axis.

16. The antenna of claim 1, further comprising a longitudinally extending chassis, said mounting plate being attached to said chassis.

17. The antenna of claim 16, further comprising a longitudinally extending molding that attaches to said chassis and supports said mounting plate.

18. The antenna of claim 1, further comprising a radome having integral guide rails that secure said radome to said antenna.

19. The antenna of claim 18, further comprising a longitudinally extending chassis, wherein said guide rails secure said radome to said chassis.

20. The antenna of claim 1, wherein said mounting plate is a ground plane comprised of metal.

21. An antenna for transmitting and receiving electromagnetic signals comprising:

a mounting plate having a longitudinal axis;

a plurality of staggered dipole radiating elements projecting outwardly from a surface of said mounting plate, each of said radiating elements including a balanced orthogonal pair of dipoles aligned at first and second predetermined angles with respect to said longitudinal axis, forming crossed dipole pairs; and

an unbalanced feed network electromagnetically coupled to said radiating elements.

22. The antenna of claim 21, further comprising a plurality of microstrip hooks, each of said microstrip hooks being positioned adjacent to, and spaced from, each of said dipoles by a clip.

23. The antenna of claim 21, wherein said feed network includes microstrip transmission lines that extend along said mounting plate and are spaced from said mounting plate by a plurality of clips.

24. The antenna of claim 21, wherein said staggered radiating elements are aligned in a first longitudinally extending row and a second longitudinally extending row on said mounting plate, the radiating elements in each of said rows being longitudinally separated from each other by a distance D, said radiating elements in said first row being longitudinally separated from said radiating elements in the second row by a distance equal to approximately D/2.

25. The antenna of claim 21, further including a longitudinally extending chassis, said mounting plate being attached to said chassis.

26. The antenna of claim 25, further comprising a longitudinally extending molding that attaches to said chassis and supports said mounting plate.

27. The antenna of claim 25, wherein said feed network extends along said mounting plate and is disposed between said chassis and said mounting plate.

28. The antenna of claim 21, wherein said radiating elements are comprised of metal.

29. The antenna of claim 21, wherein said radiating elements are attached to said mounting plate such that each of said pairs of dipoles are generally orthogonal to said surface of said mounting plate.

30. The antenna of claim 21, wherein each of said radiating elements includes four half dipoles and each of said radiating elements includes a base with four feet.

31. The antenna of claim 30, wherein each of said feet are attached to said mounting plate by a cold forming method.

32. The antenna of claim 21, wherein said dipoles comprise two half dipoles, each of said half dipoles having a generally inverted L-shaped profile, a portion of said generally L-shaped profile forming a vertical support.

33. The antenna of claim 32, further including a balun comprised of one of said microstrip hooks and said vertical support for each half dipole.

34. The antenna of claim 32, wherein each said microstrip hook is separated from said vertical support for each half dipole by an air dielectric.

35. The antenna of claim 21, wherein each of said microstrip hooks is generally shaped like an inverted U.

36. The antenna of claim 21, whereby said first predetermined angle is substantially equal to +45 degrees with respect to said longitudinal axis and said second predetermined angle is substantially equal to -45 degrees with respect to said longitudinal axis.

37. The antenna of claim 21, further comprising a radome having integral guide rails that secure said radome to said antenna.

38. The antenna of claim 37, further comprising a longitudinally extending chassis, wherein said guide rails secure said radome to said chassis.

39. The antenna of claim 21, wherein said mounting plate is a ground plane comprised of metal.

40. An antenna for transmitting and receiving electromagnetic signals comprising:

a mounting plate having a longitudinal axis;

a plurality of dipole radiating elements projecting outwardly from a surface of said mounting plate, each of said elements including a balanced orthogonal pair of dipoles aligned at first and second predetermined angles with respect to said longitudinal axis, forming crossed dipole pairs;

a longitudinally extending chassis, said mounting plate being attached to said chassis; and

an unbalanced feed network electromagnetically coupled to said radiating elements, said feed network extending along said mounting plate and being disposed between said chassis and said mounting plate.

41. The antenna of claim 40, further comprising a longitudinally extending molding that attaches to said chassis and supports said mounting plate.

42. The antenna of claim 40, further comprising a plurality of microstrip hooks, each of said microstrip hooks being positioned adjacent to, and spaced from, each of said dipoles by a clip.

43. The antenna of claim 42, wherein each of said microstrip hooks is generally shaped like an inverted U.

44. The antenna of claim 40, wherein said feed network extends along said mounting plate and is spaced from said mounting plate by a plurality of clips.

45. The antenna of claim 40, wherein said radiating elements are staggered such that they are aligned in a first longitudinally extending row and a second longitudinally extending row on said mounting plate, the radiating elements in each of said rows being longitudinally separated from each other by a distance D, said radiating elements in said first row being longitudinally separated from said radiating elements in the second row by a distance equal to approximately D/2.

46. The antenna of claim 40, wherein said radiating elements are attached to said mounting plate such that each of said pairs of dipoles are generally orthogonal to said surface of said mounting plate.

47. The antenna of claim 40, wherein each of said radiating elements includes four half dipoles and each of said radiating elements includes a base with four feet.

48. The antenna of claim 47, wherein each of said feet are attached to said mounting plate by a cold forming method.

49. The antenna of claim 40, wherein said dipoles comprise two half dipoles, each of said half dipoles having a generally inverted L-shaped profile, a portion of said generally L-shaped profile forming a vertical support.

50. The antenna of claim 49, further including a balun comprised of a microstrip hook and said vertical support for each half dipole.

51. The antenna of claim 50, wherein said microstrip hook is separated from said vertical support for each half dipole by an air dielectric.

52. The antenna of claim 40, whereby said first predetermined angle is substantially equal to +45 degrees with respect to said longitudinal axis and said second predetermined angle is substantially equal to -45 degrees with respect to said longitudinal axis.

53. The antenna of claim 40, further comprising a radome having integral guide rails that secure said radome to said antenna.

54. A method for assembling an antenna that receives and transmits electromagnetic signals comprising:

providing a mounting plate having a length and a longitudinal axis along said length;

providing a plurality of dipole radiating elements projecting outwardly from a surface of said mounting plate, each of said elements including a balanced orthogonal pair of dipoles aligned at first and second predetermined angles with respect to said longitudinal axis, forming crossed dipole pairs;

attaching said mounting plate to a longitudinally extending chassis; and

electromagnetically coupling an unbalanced feed network to said radiating elements, said feed network extending along said mounting plate and being disposed between said chassis and said mounting plate.

55. The method of claim 54, comprising the further step of spacing said feed network from said mounting plate by a plurality of clips.

56. The method of claim 54, further comprising the step of positioning a microstrip hook adjacent to one of said dipoles by a clip that spaces said microstrip hook from said dipole.

57. The method of claim 54, comprising the further steps of forming each of said dipole pairs from metal plates and attaching said plates to said mounting plate so said plates are generally orthogonal to said surface of said mounting plate.

58. The method of claim 54, further comprising the step of providing a longitudinally extending molding that attaches to said chassis and supports said mounting plate.

59. The method of claim 54, further comprising the step of staggering said radiating elements such that they are aligned in a first longitudinally extending row and a second longitudinally extending row on said mounting plate, the radiating elements in each of said rows being longitudinally separated from each other by a distance D, said radiating elements in said first row being longitudinally separated from said radiating elements in the second row by a distance equal to approximately D/2.

60. The method of claim 54, further comprising the steps of attaching said radiating elements to said mounting plate such that each of said pairs of dipoles are generally orthogonal to said surface of said mounting plate.

61. The method of claim 54, wherein each of said radiating elements includes four half dipoles and each of said radiating elements includes a base with four feet, further comprising the step of attaching each of said feet to said mounting plate by a cold forming method.

62. The method of claim 54, further comprising the step of attaching a radome, having integral guide rails, to said antenna.

FIELD OF THE INVENTION

The present invention relates generally to the field of antennas. More particularly, it concerns a dual polarized base station antenna for wireless telecommunication systems.

BACKGROUND OF THE INVENTION

Base stations used in wireless telecommunication systems have the capability to receive linear polarized electromagnetic signals. These signals are then processed by a receiver at the base station and fed into a telephone network. In practice, the same antenna which receives the signals can also be used to transmit signals. Typically, the transmitted signals are at different frequencies than the received signals.

A wireless telecommunication system suffers from the problem of multi-path fading. Diversity reception is often used to overcome the problem of severe multipath fading. A diversity technique requires at least two signal paths that carry the same information but have uncorrelated multi-path fadings. Several types of diversity reception are used at base stations in the telecommunications industry including space diversity, direction diversity, polarization diversity, frequency diversity and time diversity. A space diversity system receives signals from different points in space requiring two antennas separated by a significant distance. Polarization diversity uses orthogonal polarization to provide uncorrelated paths.

As is well-known in the art, the sense or direction of linear polarization of an antenna is measured from a fixed axis and can vary, depending upon system requirements. In particular, the sense of polarization can range from vertical polarization (0 degrees) to horizontal polarization (90 degrees). Currently, the most prevalent types of linear polarization used in systems are those which use vertical/horizontal and +45°/-45° polarization (slant 45°). However, other angles of polarization can be used. If an antenna receives or transmits signals of two polarizations normally orthogonal, they are also known as dual polarized antennas.

An array of slant 45° polarized radiating elements is constructed using a linear or planar array of crossed dipoles located above a ground plane. A crossed dipole is a pair of dipoles whose centers are co-located and whose axes are orthogonal. The axes of the dipoles are arranged such that they are parallel with the polarization sense required. In other words, the axis of each of the dipoles is positioned at some angle with respect to the vertical or longitudinal axis of the antenna array.

One problem associated with a crossed dipole configuration is the interaction of the electromagnetic field of each crossed dipole with the fields of the other crossed dipoles and the surrounding structures which support, house and feed the crossed dipoles. As is well known in the art, the radiated electromagnetic (EM) fields surrounding the dipoles transfer energy to each other. This mutual coupling influences the correlation of the two orthogonally polarized signals. The opposite of coupling is isolation, i.e., coupling of -30 dB is equivalent to 30 dB isolation.

Dual polarized antennas have to meet a certain port-to-port isolation specification. The typical port-to-port isolation specification is 30 dB or more. The present invention increases the port-to-port isolation of a dual polarized antenna. This isolation results from the phase-adjusted re-radiated energy that cancels with the dipole mutual coupling energy.

Generally, dual polarized antennas must meet the 30 dB isolation specification in order to be marketable. Not meeting the specification means the system integrator might have to use higher performance filters which cost more and decrease antenna gain. The present invention overcomes these concerns because it meets or exceeds the 30 dB isolation specification. Additionally, dual polarized antennas generally must achieve 10 dB cross polarization discrimination at 60 degrees in order to be marketable, i.e., must achieve 10 dB cross polarization discrimination at a position perpendicularly displaced from the central axis of the antenna and 60 degrees away from the plane intersecting that axis. The present invention provides a means to meet the 10 dB cross polarization discrimination specification.

Another problem associated with prior antenna arrays is their size. Prior antenna arrays provided a plurality of radiating elements along the length of the antenna. Therefore, the length of the antenna was dictated by the number and spacing of the radiating elements. Because the gain of an antenna is proportional to the number and spacing of the radiating elements, the width and height of prior antennas could not be reduced significantly without sacrificing antenna gain.

In order to prevent corrosion, there is a need for an antenna capable of preventing water and other environmental elements from impinging upon active antenna components. One solution is providing the antenna with a protective radome. However, one problem with prior antennas is the attachment of the protective radome to the antenna. Because of the manner of attachment of prior radomes, prior radome designs allow water and other environmental elements to impinge upon active antenna components, thereby contributing to antenna corrosion (e.g., the failure of sealants such as caulk). Furthermore, because those prior radomes do not maintain seal integrity over both time and thermal excursions, such radomes allow water and other environmental contaminants to enter the antenna.

Moreover, the visual impact of base station towers on communities has become a societal concern. It has become desirable to reduce the size of these towers and thereby lessen the visual impact of the towers on the community. The size of the towers can be reduced by using base station towers with fewer antennas. This can be achieved if dual polarized antennas and polarization diversity are used. Such systems replace systems using space diversity which requires pairs of vertically polarized antennas. Some studies indicate that, for urban environments, polarization diversity provides signal quality equivalent to space diversity. With the majority of base station sites located in urban environments, it is likely that dual polarized antennas will be used in place of the conventional pairs of vertically polarized antennas. Another way to reduce the size of the base station towers is by using smaller base station antennas. The present invention addresses the problems associated with prior antennas.

SUMMARY OF THE INVENTION

An improved antenna system is provided for transmitting and receiving electromagnetic signals comprising a mounting plate having a length and a longitudinal axis along the length. A plurality of staggered dipole radiating elements project outwardly from a surface of the mounting plate. Each of the radiating elements includes a balanced orthogonal pair of dipoles aligned at first and second predetermined angles with respect to the longitudinal axis, forming crossed dipole pairs. The mounting plate is attached to a longitudinally extending chassis. An unbalanced feed network is connected to the radiating elements. The feed network extends along the mounting plate and is spaced from the mounting plate by a plurality of clips. The feed network is disposed between the chassis and the mounting plate. A plurality of microstrip hooks are provided, each of the microstrip hooks being positioned adjacent to, and spaced from, each of the dipoles by one of the clips.

The present invention therefore provides an antenna array which produces dual polarized signals. The invention also provides an antenna capable of at least 30 dB port-to-port isolation. The invention further provides an antenna capable of at least 10 dB cross polarization discrimination at 60 degrees. The invention also provides an antenna capable of high gain while reducing the width and height of the antenna by staggering the dual polarized radiating elements contained therein. The inventive antenna incorporates an axially-compliant labyrinth seal that is both integral to the radome and maintains seal integrity over both time and thermal excursions. The antenna is capable of matching an unbalanced transmission line connected to the feed network with the balanced dipole elements. The antenna is relatively inexpensive to produce because substantially all the parts in the antenna can be mass produced at a low per unit cost; the number of unique parts and total parts is relatively small; adhesive, soldering and welding is eliminated; and the number of mechanical fasteners is minimized.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a perspective view of a top side of an antenna including a mounting plate and a plurality of staggered radiating elements;

FIG. 2 is a top view of the radiating elements, the mounting plate and a feed network for the antenna illustrated in FIG. 1;

FIG. 3 is a side view of the antenna illustrated in FIG. 2;

FIG. 4 is a partial perspective view of the radiating elements and the feed network for the antenna illustrated in FIG. 1;

FIG. 5 is a partial perspective view of radiating elements, microstrip hooks, and the feed network for the antenna illustrated in FIG. 1

FIG. 6 is a perspective view of one radiating element and its microstrip hooks for the antenna illustrated in FIG. 1

FIG. 7 is an end view of a chassis, a radome and the radiating elements for the antenna illustrated in FIG. 1;

FIG. 8 is an end view of the opposite end of the antenna illustrated in FIG. 7 showing the chassis and the radiating elements;

FIG. 9 is a perspective view of a clip used to secure the feed network and the microstrip hooks illustrated in FIGS. 1-8;

FIG. 10 is a front view of the clip illustrated in FIG. 9;

FIG. 11 is a side view of the clip illustrated in FIG. 9; and

FIG. 12 is a top view of the clip illustrated in FIG. 9.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The present invention is useful in wireless communication systems. One embodiment of the present invention operates in a range of frequencies between 800-1,000 MHz (this includes the ESMR, GSM and cellular bands of frequencies). Generally, wireless telephone users transmit an EM signal to a base station tower that includes a plurality of antennas which receive the signal transmitted by the wireless telephone users. Although useful in wireless base stations, the present invention can also be used in all types of telecommunications systems.

The antenna illustrated in FIGS. 1-5 is a 55-70 degree azimuthal, half power beam width (HPBW) antenna, i.e., the antenna achieves a 3 dB beamwidth of between 55 and 70 degrees. FIG. 1 shows an antenna array 10 of crossed, dual polarized dipole radiating elements 11a-n that are connected to a mounting plate 12. The mounting plate 12 is a metal ground plane and, as shown in FIG. 7, has a first side 14 and a second side 16. A longitudinally extending chassis 52 houses the mounting plate 12 and the radiating elements 11a-n. A longitudinally extending molding 70 attaches to the chassis 52 and supports the mounting plate 12. The number of radiating elements, the amount of power presented to the feed network and the composition and dimensions of the radiating elements and the mounting plate all contribute to the radiation pattern generated by the antenna. Preferably, the radiating elements 11a-n and the mounting plate 12 are composed of a metal such as aluminum. However, other metals such as copper or brass can be used to construct the radiating elements 11a-n and the mounting plate 12.

It will be understood by those skilled in the art that the gain of the antenna is proportional to the number of staggered radiating elements present in the array and the spacing of the elements. In other words, increasing the number of radiating elements in the antenna 10 increases the gain while decreasing the number of radiating elements reduces the antenna's gain. Therefore, although 14 radiating elements are illustrated, the number of radiating elements can be increased to increase the gain. Conversely, the number of radiating elements can be decreased to reduce the gain. The gain of the antenna 10 is maximized due to the use of dipole radiating elements 11a-n which are efficient radiators and by using an efficient microstrip feed network 31.

The radiating elements 11a-n transmit and receive EM signals and are comprised of pairs of dipoles 18a and 18b, 20a and 20b, 22a and 22b, 24a and 24b, 26a and 26b, 28a and 28b, 30a and 30b, 32a and 32b, 34a and 34b, 36a and 36b, 38a and 38b, 40a and 40b, 42a and 42b, and 44a and 44b, respectively. The radiating elements 11a-n form angles of +45 degrees and -45 degrees with respect to the longitudinal axis 13a or 13b, respectively. Each of the radiating elements 11a-n receives signals having polarizations of +45 degrees and -45 degrees. That is, the axes of the dipoles are arranged such that they are parallel with the polarization sense required. In the illustrated embodiment of FIG. 1, the slant angles +α and -α are +45 degrees and -45 degrees, respectively. Although shown with slant angles of +45 degrees and 45 degrees, it will be understood by those skilled in the art that these angles can be varied to optimize the performance of the antenna. Furthermore, the angles +α and -α need not be identical in magnitude. For example, +α and -α can be +30 degrees and -60 degrees, respectively. In the illustrated embodiment of FIG. 1, one dipole in each of the radiating elements 11a-n receives signals having polarizations of +45 degrees while the other dipole in each of the radiating elements 11a-n receives signals having polarizations of -45 degrees.

As illustrated in FIG. 5, the feed network 31 comprises two branches 31a and 31b. Branch 31a is electromagnetically coupled to each of the parallel dipoles 18a, 20a, 22a, 24a, 26a, . . . , and 44a by a microstrip hook adjacent to each of the respective dipoles. Branch 31b is electromagnetically coupled to each of the parallel dipoles 18b, 20b, 22b, 24b, 26b, . . . , and 44b by a microstrip hook adjacent to each of the respective dipoles. The received signals from parallel dipoles 18a, 20a, 22a, 24a, 26a, . . . , and 44a are distributed to a receiver using branch 31a for that polarization. Likewise, the received signals from parallel dipoles 18b, 20b, 22b, 24b, 26b, . . . , and 44b are distributed to a receiver using branch 31b for the other polarization. As illustrated in FIGS. 7-8, the feed network 31 extends along the mounting plate 12 and is spaced below the second side 16 of the mounting plate 12 by a plurality of clips 50. The feed network 31 is located between the mounting plate 12 and the chassis 52 in order to isolate the feed network 31 from the radiating elements 11a-n and to substantially reduce the amount of EM radiation from the feed network 31 that escapes from the antenna 10. The feed network 31 distributes the received signals from the radiating elements 11a-n to a diversity receiver for further processing. Each of the radiating elements 11a-n can also act as a transmitting antenna.

Each dipole is comprised of a metal such as aluminum. Each dipole includes two half dipoles. For example, as illustrated in FIG. 5, the dipole 42b includes half dipoles 42b' and 42b". Each of the half dipoles has a generally inverted L-shaped profile, as illustrated in FIG. 5. The four half dipoles that comprise one radiating element are all physically part of the same piece of metal, as illustrated in FIG. 6, and are all at earth ground at DC. However, each of the two dipoles that comprise a radiating element operate independently at RF. As shown in FIG. 5, each half dipole is attached to the other three half dipoles at the base 46 of each radiating element. The base 46 includes four feet 48 that allow the radiating element to be attached to the mounting plate 12 (shown in FIG. 5 and 6). The radiating elements are attached to the mounting plate 12 by a cold forming process developed by Tox Pressotechnik GmbH of Weingarten, Germany (the cold forming process). The cold forming process deforms the four metal feet 48 and the metal mounting plate 12 together at a button. The cold forming process uses pressure to lock the metal of the feet 48 and the metal of the mounting plate 12 together. This process eliminates the need for mechanical fasteners to secure the radiating elements to the mounting plate 12.

The present invention also improves the cross polarization discrimination of antenna 10. As illustrated in FIG. 5, a downwardly extending vertical portion 57 is provided at the distal end of each generally L-shaped dipole. The vertical portion 57 improves the cross polarization discrimination of the antenna such that at least 10 dB cross polarization discrimination is achieved at 60 degrees.

A portion of each generally L-shaped half dipole forms a vertical support. For example, as illustrated in FIG. 5, half dipole 42b' includes vertical support 54 and half dipole 42b" includes vertical support 55. A microstrip hook is attached to, and spaced from, each of the dipoles by one of the clips 50. The microstrip hooks electromagnetically couple each dipole to the feed network 31. For example, adjacent dipole 42b is microstrip hook 56 which is integral with branch 31b of the feed network 31. A balanced/unbalanced (balun) transformer 58 is provided for each of the dipoles 18a, 18b, 20a, 20b, 22a, 22b, 24a, 24b, 26a, 26b, . . . , 44a and 44b. The general operation of a balun is well known in the art and is described in an article by Brian Edward & Daniel Rees, A Broadband Printed Dipole with Integrated Balun, MICROWAVE JOURNAL, May 1987, at 339-344, which is incorporated herein by reference. Each of the baluns 58 comprise one microstrip hook and the vertical support for each half dipole. For example, as illustrated in FIG. 5, the dipole 42b includes the balun 58 which comprises the microstrip hook 56 and the vertical supports 54 and 55. Each of the microstrip hooks 56 is generally shaped like an inverted U. However, in order to achieve a symmetrical pair of crossed dipoles, one leg of the inverted U is substantially longer than the other leg. The baluns 58 match the unbalanced transmission lines connected to the feed network 31 with the balanced pairs of dipole elements 18a and 18b, 20a and 20b, 22a and 22b, 24a and 24b, 26a and 26b, . . . , and 44a and 44b, respectively. The microstrip hooks 56 are each integrally connected to the feed network 31. The plurality of microstrip hooks 56 are each attached to, and spaced from, each of their respective dipoles by one of the clips 50. The clips 50 are composed of a dielectric material such as, for example, a glass fiber loaded polypropylene. As illustrated in FIGS. 9-12, each of the clips 50 include two generally U-shaped upper projections 49 extending upwardly from a base 51 and two generally U-shaped lower projections 53 extending downwardly from the base 51. The lower projections 53 allow the clips 50 to attach to, for example, one of the dipoles or the mounting plate. The upper projections 49 allow the clips 50 to attach, for example, the feed network 31 to the mounting plate 12 or one of the microstrip hooks 56 to one of the dipoles.

FIG. 7 illustrates a radome 60 that encloses the antenna array 10. The radome 60 includes two longitudinally extending bottom edges 62 that are integrally formed with the radome 60. The chassis 52 includes two longitudinally extending rails 63. The radome 60 is secured to the antenna 10 by, for example, sliding the radome 60 onto the chassis 52 such that the longitudinally extending bottom edges 62 are in spring engagement with the rails 63 of the chassis 52. Alternatively, the radome 60 is secured to the antenna 10 by snapping the bottom edges 62 into the rails 63 of the chassis. The tight, frictional engagement between the bottom edges 62 and the rails 63 inhibits water and other environmental elements from entering the antenna, to prevent corrosion of the antenna 10. The guide rails secure the radome 60 to the antenna 10 and prevent movement of the radome 60 with respect to the chassis 52 in two directions, i.e., laterally and vertically away from the mounting plate 12. End caps 73 snap onto the ends of the antenna 10 to seal in the radiating elements 11a-n and to protect the antenna 10 from adverse environmental conditions. Extending through the chassis 52 approximately halfway down the length of the antenna 10 are a pair of connectors 64 that electrically connect branch 31a and branch 31b of the feed network 31 with, for example, an external receiver or transmitter. Alternatively, the connectors 64 may be located in one of the end caps of the antenna 10. A pair of integrated mounting bracket interfaces 65 extend along the exterior of the chassis 52 and allow the antenna 10 to be connected to a base station tower.

In the illustrated embodiment of FIG. 1, the 14 crossed dipole radiating elements 11a-n are attached to a mounting plate 2.6 m long by 0.25 m wide. The antenna 10 operates in a range of frequencies between 800-1,000 MHz (this includes the ESMR, GSM and cellular bands of frequencies). The longitudinal axes 13a and 13b extend along the longitudinal length of the array 10. Seven of the radiating elements (11a, 11c, 11e, 11g, 11i, 11k, and 11m) are aligned along the longitudinal axis 13a while the other seven radiating elements (11b, 11d, 11f, 11h, 11j, 11l, and 11n) are aligned along the longitudinal axis 13b. Thus, the radiating elements are aligned in a first longitudinally extending row 66 and a second longitudinally extending row 68 on the mounting plate 12. Each radiating element in the first row 66 is staggered from each of the radiating elements in the second row 68. As illustrated in FIG. 1, the radiating elements in row 66 and the radiating elements in row 68 are each longitudinally separated from each other by a distance D. However, the radiating elements in the first row 66 are longitudinally separated from the radiating elements in the second row 68 by a distance equal to approximately D/2.

The antenna of the present invention includes dual polarized radiating elements that produce two orthogonally polarized signals. The present invention further provides an antenna array comprised of crossed dipoles. The invention comprises a plurality of staggered radiating elements that provide the antenna with high gain while reducing the width and height of the antenna. The elements of the inventive antenna improve the isolation between the EM fields produced by the crossed dipoles. The downwardly extending vertical portion at the distal end of each generally L-shaped dipole improves the cross polarization discrimination of the antenna such that at least 10 dB cross polarization discrimination is achieved at 60 degrees. The antenna also minimizes the number of antennas required in a wireless telecommunication system, thereby providing an aesthetically pleasing base station that is of minimum size. The inventive antenna incorporates an axially-compliant labyrinth seal that is both integral to the radome and maintains seal integrity over both time and thermal excursions. The antenna is less expensive to produce because substantially all the parts in the antenna can be mass produced at a low per unit cost; the number of unique parts and total parts is relatively small; adhesive, soldering and welding is eliminated; and the number of mechanical fasteners is minimized.

While the present invention has been described with reference to one or more preferred embodiments, those skilled in the art will recognize that many changes may be made thereto without departing from the spirit and scope of the present invention which is set forth in the following claims.